Production from an oil well is pumped from the oil well into a production tank. Each production tank may, and usually does, contain varying amounts of six substances: sand, oil, water, oil/water emulsion, foam, and gas. If there is an excessive quantity of any one of these substances, remedial action should be taken. Knowing the over all fluid level in the production tank is not sufficient, as it does not indicate the relative quantities of the substances.
U.S. Pat. No. 6,959,599 (Feldstein et al.) entitled “Level detector for storage tanks for fluids”, discloses a level detector which can detect the difference between a mass of fluid and the void volume above it. The Feldstein et al. level detector operates upon a theory of differential rate of heat transfer. This Feldstein et al. level detector would be effective to indicate total fluid volume, but would not be effective, by itself, in determining the relative quantities of the substances. With oil well production tanks the analysis is further complicated by the presence of a fire tube, which heats the fluids to promote separation and, in doing so, maintains the fluids within a relatively homogeneous temperature profile.